A various solenoid valve that has a valve seat disposed between a first flow passage and a second flow passage, and can connect and disconnect the first flow passage and the second flow passage by sliding a valve body for contacting/detaching a valve body to the valve seat is known so far.
For example, a permanently-opened type solenoid valve disclosed in Japanese Patent Application Laid-Open Publication No. 2002-347597 is known. This type of the solenoid valve has a moving core, which is attracted when a coil is energized, disposed in a bottomed cylindrical sleeve slidably.
A valve body is disposed so as to contact an end surface of the moving core, and the valve body slides in a direction where a valve seat is seated by energizing the coil.
Moreover, the valve body is forced to a direction away from the valve seat by an applied force of a spring, as well as a fluid that flows in from a first flow passage and acts onto the valve body in the direction away from the valve seat.
Moreover, in the solenoid valve of such a composition, a permanently-opened type differential-pressure-controlled solenoid valve that adjusts a differential pressure between upstream and downstream of the solenoid valve linearly by controlling an amount of energization of the coil is also known.
However, when adjusting the differential pressure using a size difference (large or small) of a gap between the valve body and the valve seat by balancing the electromagnetic force and the spring force by control the amount of energization of the coil in such the past solenoid valve, the size of the gap changes due to the sliding of the valve body even by a small change of the fluid pressure.
The fluid pressure changes especially at small/low flow rates or the differential pressure between upper and lower streams is small because the fluid that flows from the first flow passage to the second flow passage through the valve seat flows out while applying the fluid pressure to the tip of the valve body.
Thus problems such that the pressure control status becomes unstable and unable to adjust the differential pressure linearly for the amount of energization of the coil arise.